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SIONlib

Scalable I/O library for parallel access to task-local files

SIONlib is a library for writing and reading binary data to/from several thousands of processors into one or a small number of physical files. For parallel access to files only the open and close functions are collective while writing and reading file can be done asynchronously. SIONlib provides a SIONlib file handle which substitutes the C file pointer.

SIONlib provides a simplified file handling for parallel programs which formerly read or write binary data in parallel into separate files (task-local files). After opening the file with SIONlib, the I/O can be done with the SIONlib equivalents to standard C-I/O functionality (fwrite -> sion_fwrite, fread -> sion_fread) which have the same syntax as their C counterparts. Instead of maintaining thousands of separate files, there is only one large file containing all data.

Given that each processor writes its data to same file, SIONlib assigns different regions (e.g., data blocks) of the file to a processor. Hence, for each processor, SIONlib needs the estimated (or known) data size which will be written to the file (chunk size). SIONlib can also handle extensions (additional chunks), if the end of a data block is reached.

Both, the estimated chunk size and file system block size are used to calculate the individual start position inside the file for each processor. Ensuring contention-free access to file system blocks enables efficient parallel writing and reading.